javascript 使用 jasmine 监视构造函数

Spy on a constructor using jasmine

提问by Mike Rifgin

I want to spy on a constructor function and tell how many times it's been called using jasmine. I'd usually do something like this to target a method of an object:

我想监视一个构造函数并告诉它使用 jasmine 被调用了多少次。我通常会做这样的事情来定位一个对象的方法：

spyOn(lib,'methodName')

but in the case I'm trying to spy on the actualy constructor so I've tried:

但在这种情况下，我试图监视实际的构造函数，所以我尝试过：

spyOn(lib);


 it('lib should be instantiated for each matching element', function () {
    spyOn(lib);
    expect(lib.calls.count()).toEqual(2);
});

Unfortunately this just gives me an error in the console:

不幸的是，这只会在控制台中给我一个错误：

"Error: undefined() method does not exist in ..."

how can I spy on the constructor?

我如何监视构造函数？

回答by inf3rno

The spyOn()function can only replace object properties, so the only thing you can do is spying on the prototype. Now if you would spy on the prototype of the real class, it would interfere with the other tests, so you have to use prototypal inheritance.

该spyOn()函数只能替换对象属性，因此您唯一能做的就是监视原型。现在如果你要窥探真实类的原型，它会干扰其他测试，所以你必须使用原型继承。

You can do something like this :

你可以这样做：

var mockClass = function (Subject) {
    var Surrogate = function () {
        Surrogate.prototype.constructor.apply(this, arguments);
    };
    Surrogate.prototype = Object.create(Subject.prototype);
    Surrogate.prototype.constructor = Subject;
    return Surrogate;
};

Some tests:

一些测试：

var My = function (a) {
    this.init(a);
};
My.prototype = {
    init: function (a) {
        this.setA(a);
    },
    setA: function (a) {
        this.a = a;
    }
};

var Mock = mockClass(My);
spyOn(Mock.prototype, "constructor").andCallThrough();
spyOn(Mock.prototype, "init");

var m = new Mock(1);

expect(Mock.prototype.init).toBe(m.init);
expect(My.prototype.init).not.toBe(m.init);
expect(m.constructor).toHaveBeenCalledWith(1);
expect(m.init).toHaveBeenCalledWith(1);
expect(m.a).toBeUndefined();
m.setA(1);
expect(m.a).toBe(1);

spyOn(Mock.prototype, "setA").andCallFake(function (a) {
    this.a = a + 1;
});
m.setA(1);
expect(m.setA).toHaveBeenCalledWith(1);
expect(m.a).toBe(2);

You cannot spy on the constructorif your code uses an x.constructorbased type checking. But I think this can happen only by integration tests, and by badly designed codes...

constructor如果您的代码使用x.constructor基于类型检查，您就无法窥探。但我认为这只能通过集成测试和设计糟糕的代码发生......